Hydrostatic transmission and power train for vehicle

ABSTRACT

A hydrostatic transmission for vehicle interposed in a drive-power transmission path between a driving power source and a driving axle for non-stepwisely changing the speed of the vehicle includes an HST housing; a hydraulic pump unit having a pump shaft with first and second ends extending in a fore-aft direction of the vehicle away from each other; a hydraulic motor unit having a motor shaft for outputting the drive power from the motor shaft whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit; a PTO unit having a PTO shaft extending in the fore-aft direction of the vehicle, the PTO shaft being operatively connected to the pump shaft; a charge pump unit for replenishing pressurized hydraulic fluid to a hydraulic circuit, the hydraulic circuit hydraulically connecting the hydraulic pump unit with the hydraulic motor unit, the charge pump unit including a charge pump body, and a charge pump case connected to the HST housing through its wall closer to the driving axle for supporting the charge pump body; the PTO shaft having an one end closer to the driving axle, the one end extending outwardly through the HST housing to have an outer extension positioned outside of the HST housing; and the charge pump case being designed so as to bearing-support the outer extension of the PTO shaft.

BACKGROUND OF THE INVENTION

Background of the Invention

The present invention relates to a hydrostatic transmission (hereinafterreferred to as HST) for vehicle that is interposed in a drive-powertransmission path between a drive power source and a driving axle, and apower train for vehicle between the drive power source and the drivingaxle.

It is known that the HST interposed in the drive-power transmission pathbetween the drive power source and the driving axle is provided with aPTO unit for driving a working device. FIG. 9(a) is a model viewillustrating a drive-power transmission in the arrangement that aconventional HST with a PTO unit is applied to a vehicle that has afront axle serving as a driving axle and is provided on the front sideof the vehicle with a mower or any other working device.

As illustrated in FIG. 9(a), the HST with the PTO unit includes ahydraulic pump unit with a pump shaft operatively connected to the drivepower source, a hydraulic motor unit with a motor shaft for outputtingthe drive power through the motor shaft whose speed is non-stepwiselyvaried in cooperation with the hydraulic pump unit, a PTO unit with aPTO shaft operatively connected to the pump shaft, and an HST housingaccommodating the hydraulic pump unit, the hydraulic motor unit and thePTO unit, in which the PTO shaft has a front end extending forwardlythrough the HST housing.

In some cases, a demand exists for a wide range of speed change of thedriving axle and reduced load applied to the HST serving as a main speedchange device. In that case, a mechanical transmission serving as anauxiliary speed change device is additionally interposed between the HSTas the main speed change device and the driving axle. FIG. 9(b) is amodel view illustrating a drive-power transmission path between thedrive power source and the driving axle (front axle) in which the HSTwith the PTO unit and the mechanical transmission are interposed.

Here, comparing the distance between the front end of the PTO shaft andthe front axle (hereinafter referred to distance L) in the arrangementof FIG. 9(a) with the distance L of the arrangement of FIG. 9(b), theformer arrangement is: L=L1, and the latter arrangement is: L=L1+L2, inwhich L2 represents the length of the mechanical transmission withrespect to a fore-aft direction of the vehicle.

The front end of the PTO shaft is connected to the mower or any otherworking device via transmission parts such as a connecting rod with auniversal joint. Accordingly, the variation of the distance Lnecessitates the modification of the transmission parts, the workingdevice and any other associated parts.

Taking for example the vehicle that is provided with the mower as theworking device having an elevation function, the variation of thedistance L invites not only variation of the length of the connectingrod but also variation of the elevation height of the mower.

That is, since the front end of the PTO shaft serves as a fulcrum forthe mower during the upward or downward movement, a simply elongated theelongation of the transmission shaft by L2 simply causes the mower tohave a different elevation height. Therefore, in order to equalize theelevational height of the mower between the vehicles of FIGS. 9(a) and9(b), there arises a necessity to modify a hydraulic piston forelevation of the mower or any other parts.

There thus exist the arrangements with only the main speed change deviceinterposed in the drive-power transmission path, and both the main andauxiliary speed change devices interposed therein. In eitherarrangement, a demand exists for non-variation of the distance betweenthe front end of the PTO shaft and the driving axle. In other words, ademand exists for the arrangement holding the distance between the frontend of the PTO shaft and the driving axle constant regardless of thedistance between the driving axle and the main speed change device.

The auxiliary speed change device is an optional member that is providedaccording to a specification of the vehicle. Therefore, regarding partsconstituting the power train between the drive power source and thedriving axle excepting the auxiliary speed change device, it ispreferable to render those parts commonly usable as many as possible forboth arrangements with and without the auxiliary speed change device.

The present invention has been conceived in consideration of the aboveprior arts. It is an object of the present invention to provide an HSTthat is capable of effectively limiting the variation in distancebetween an end of the PTO shaft and the driving axle, even if thedistance between the driving axle and the HST is varied.

It is another object of the present invention to provide a power trainfor vehicle that is capable of being adapted to or matching arrangementswith or without the auxiliary speed change device or modifications ofthe same, or meeting any other demands.

SUMMARY OF THE INVENTION

To achieve the above objects, there is provided a hydrostatictransmission for vehicle interposed in a drive-power transmission pathbetween a driving power source and a driving axle for non-stepwiselychanging the speed of the vehicle. The hydrostatic transmission includesan HST housing; a hydraulic pump unit disposed within the HST housingand having a pump shaft with first and second ends extending in afore-aft direction of the vehicle away from each other, in which thefirst end is positioned closer to the driving axle, and the second endis positioned away from the driving axle and operatively connected tothe driving power source; a hydraulic motor unit disposed within the HSThousing and having a motor shaft for outputting the drive power from themotor shaft whose speed is non-stepwisely varied in cooperation with thehydraulic pump unit; a PTO unit disposed within the HST housing andhaving a PTO shaft extending in the fore-aft direction of the vehicle,the PTO shaft being operatively connected to the pump shaft; a chargepump unit for replenishing pressurized hydraulic fluid to a hydrauliccircuit, the hydraulic circuit hydraulically connecting the hydraulicpump unit with the hydraulic motor unit, the charge pump unit includinga charge pump body that is driven through the first end of the pumpshaft, and a charge pump case connected to the HST housing through itswall closer to the driving axle for supporting the charge pump body; thePTO shaft having an one end closer to the driving axle, the one endextending outwardly through the HST housing to have an outer extensionpositioned outside of the HST housing; and the charge pump case beingdesigned so as to bearing-support the outer extension of the PTO shaft.

According to the HST having the above arrangement, the outer extensionof the PTO shaft is bearing-supported by the charge pump case that isconnected to the HST housing. Therefore, the variation in distancebetween the second end of the PTO shaft and the driving axle can beeffectively limited, even if the distance between the driving axle andthe HST is varied. As a result, the common working device that is driventhrough the PTO shaft and the common drive power transmission mechanismfor transmitting the drive power to the working device can be used forboth the arrangements where the HST only is interposed in thedrive-power transmission path and where the HST, and the mechanicaltransmission and/or the PTO device are interposed therein.

In the hydrostatic transmission having the above arrangement, the PTOunit preferably includes a hydraulic clutch device for on/off of thedriver power transmission from the pump shaft to the PTO shaft. Thecharge pump unit also preferably includes a flow divider for dividingthe pressurized fluid from the charge pump body to the one forreplenishment to the hydraulic circuit and the other for actuation ofthe hydraulic clutch device, in which the flow divider is disposedwithin the charge pump case.

The first end of the pump shaft preferably extends outwardly through thecharge pump case. The hydrostatic transmission also preferably includesan auxiliary pump unit detachably connected to the pump case forreceiving the driving power through the first end of the pump shaft.

According to another aspect of the present invention, there is provideda power train for vehicle between a driving power source and a drivingaxle. The power train includes a transfer device disposed between a mainspeed change device that is operatively connected to the driving powersource and a differential gear device that transmits the drive power tothe driving axle. The transfer device includes a driving shaft and anoutput shaft. The driving shaft is disposed along a main drive-powertransmission axis and operatively connected to a main output shaft ofthe main speed change device. The main transmission axis is coaxial withthe main output shaft, and the output shaft is disposed along the maindrive-power transmission axis for outputting the drive power to thedifferential gear device. With this arrangement, the speed can bestepwisely changed between the driving shaft and the output shaft.

With the power train of the above arrangement, the speed change rangeavailable in the drive-power transmission path can easily be widened.Also, by replacing the transfer device with a different one, thespecification of the power train can easily be modified. That is, merelymounting or dismounting the transfer device, or modifying the sameachieves matching to various specifications of the vehicle.

According to another aspect of the present invention, there is provideda power train for vehicle between a driving power source and a drivingaxle. The power train includes a transfer device disposed between a mainspeed change device that is operatively connected to the driving powersource and a differential gear device that transmits the drive power tothe driving axle. The transfer device includes a driving shaft and anoutput shaft. The driving shaft is disposed along a main drive-powertransmission axis and operatively connected to a main output shaft ofthe main speed change device, in which the main transmission axis iscoaxial with the main output shaft. The output shaft is disposed alongthe main drive-power transmission axis for outputting the drive power tothe differential gear device, in which the drive power is transmittedbetween the driving shaft and the output shaft. The transfer device alsoincludes an extension extending past the main speed change device in thedirection orthogonal to the main drive-power transmission axis, a PTOshaft supported on the extension in such a manner as to be substantiallyparallel to the main drive-power transmission axis, and a drive-powertransmission mechanism for transmitting the drive power synchronizedwith the output shaft to the PTO shaft.

With the power train having the above arrangement, the PTO shaft thattakes off the drive power synchronized with the driving axle can beeffectively prevented from interfering with the main speed changedevice. Thus, the drive-power transmission mechanism disposed on thedownstream side of the PTO shaft can be relatively flexibly designed.

In the power train having the above arrangement, the drive-powertransmission mechanism preferably includes a driven shaft that isdisposed between the main drive-power transmission axis and the PTOshaft in parallel thereto, a first gear train for transmitting the drivepower from the driving shaft to the driven shaft at a predeterminedspeed reducing ratio, a second gear train for transmitting the drivepower from the driven shaft to the output shaft at the same speedreducing ratio as the predetermined speed reducing ratio, and a thirdgear train for transmitting the drive power from the driven shaft to thePTO shaft at the same speed reducing ratio as the predetermined speedreducing ratio.

With the power train having the above arrangement, the PTO shaft caneffectively be rotated in synchronization with the output shaft, whilesharing in part the common parts between the drive-power transmissionline for the PTO system and the drive-power transmission line for thevehicle run. Thus, the transfer device can be manufactured compact ascompared with the arrangement that the PTO drive power is taken offthrough the output shaft of the transfer device.

The power train preferably has the first gear train including an idlegear that is relatively rotatably supported on the driving shaft, and afirst driven gear that is relatively non-rotatably supported on thedriven shaft to be meshed with the idle gear; the second gear trainincluding a second driven gear that is relatively non-rotatablysupported on the driven shaft, and an output gear that is relativelynon-rotatably supported on the output shaft to be meshed with the seconddriven gear; the third gear train including a PTO gear that is meshedwith either one of the first and second driven gears to transmit thedrive power to the PTO shaft. In this arrangement, the speed reducingratio of the first driven gear with respect to the idle gear, the speedreducing ratio of the output gear with respect to the second drivengear, and the speed reducing ratio of the PTO gear with respect to thefirst or second driven gear are the same.

The transfer device preferably includes a clutch member that isrelatively non-rotatably and axially slidably supported on the drivingshaft. The clutch member is adapted to selectively take a positionenabling connection between the driving shaft and the idle gear, aposition enabling connection between the driving shaft and the outputshaft, and a neutral position between both the positions, enablingshutdown of the drive-power transmission from the driving shaft to theoutput shaft.

With the arrangement above, through shifting operation of the clutchmember, the output shaft and the PTO shaft can be brought intonon-outputting state, or the output shaft and the PTO shaft can havespeeds changeable in synchronization with each other.

The transfer device preferably includes a counter shaft that is disposedcoaxially with the PTO shaft and a slider that is relativelynon-rotatably and axially slidably on the PTO shaft and the countershaft. The PTO gear is supported on the counter shaft via a one-wayclutch. The slider is adapted to selectively take a non-outputtingposition enabling disconnection between the counter shaft and the PTOshaft, a forced outputting position enabling connection between thecounter shaft and the PTO shaft while being in meshing engagement withthe PTO gear, and a middle position between the non-outputting positionand the forced outputting position, enabling connection between thecounter shaft and the PTO shaft while being out of the meshingengagement with the PTO gear.

With the arrangement above, it is possible to easily change theoutputting state of the PTO shaft. Specifically, through shiftingoperation of the slider, it is possible to easily change the mode of thePTO shaft between a mode enabling forced synchronization of the PTOshaft with the output shaft, a mode enabling shutdown of the drive powertransmission from the output shaft to the PTO shaft when the PTO shaftrotates at a higher speed than the output shaft, and a mode enablingshutdown of the drive power transmission to the PTO shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, and other objects, features and advantages of the presentinvention will become apparent from the detailed description thereof inconjunction with the accompanying drawings wherein.

FIG. 1 is a model view illustrating a power train for a vehicle to whichone embodiment of an HST of the present invention is applied.

FIG. 2 is a hydraulic circuit diagram of the vehicle illustrated in FIG.1.

FIG. 3 is a transverse plan view of the HST illustrated in FIG. 1.

FIG. 4 is a cross-section taken along lines IV—IV in FIG. 3.

FIG. 5 is a view as viewed along lines V—V in FIG. 3.

FIG. 6 is a cross-section taken along lines VI—VI in FIG. 3.

FIG. 7 is a cross-section taken along VII—VII in FIG. 3.

FIG. 8 is a view as viewed along lines VIII—VIII in FIG. 3.

FIG. 9(a) is the model view illustrating a power train in thearrangement that a conventional HST with a PTO unit is applied to avehicle that has a front axle serving as a driving axle and is providedon the front side of the vehicle with a working device such as a mower.

FIG. 9(b) is the model view illustrating a power train between the drivepower source and the driving axle (front axle) in which the HST with thePTO unit and the mechanical transmission are interposed.

FIG. 10 is a perspective view of the HST, the mechanical transmissionand a front axle as viewed obliquely from behind.

FIG. 11 is a cross-section of the mechanical transmission taken alongthe drive-power transmission path of the mechanical transmission.

FIG. 12 is a cross-section of the mechanical transmission including amoving part of its range-shift arm.

FIG. 13 is a longitudinal cross-section of the mechanical transmissionwith its stepped cross-section as viewed from behind.

FIG. 14 is a cross-section with the mechanical transmission removed andthe HST directly connected to a differential gear device.

FIG. 15 is a cross-section with the drive-power transmission equippedwith the PTO unit mounted in replacement of the mechanical transmission.

FIG. 16 is a cross-section taken along lines XVI—XVI in FIG. 3.

FIG. 17 is a cross-section taken along lines XVII—XVII in FIG. 8 with anoutput adjusting member lying at neutral position.

FIG. 18 is a cross-section taken along lines XVII—XVII in FIG. 8 withthe output adjusting member lying at a maximum output position in thevehicle advancing direction.

FIG. 19 is a transverse plan view of an HST equipped with a singlecharge pump unit.

FIG. 20 is a cross-section taken along lines XX—XX in FIG. 19.

FIG. 21 is a cross-section taken along lines XXI—XXI in FIG. 19.

FIG. 22 is a hydraulic circuit diagram of the vehicle to which the HSTof the FIG. 19 is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the HST for the vehicle according to the presentinvention will be hereinafter described with reference to theaccompanying drawings. This embodiment will be described by taking forexample the case that the vehicle, to which the HST is applied, has afront axle serving as a main driving axle, and is provided on the frontside of the vehicle body with a working device in the form of a mowerwith an elevation function

FIGS. 1 and 2 are respectively the power train model view and thehydraulic circuit diagram of the vehicle to which the HST is applied.FIG. 3 is the transverse plan view of the HST and FIG. 4 is thecross-section taken along lines IV—IV in FIG. 3.

As illustrated in those Figures, HST 1 is interposed in the drive-powertransmission path between drive power source 300 and the driving axle(i.e., front axle 310 in this embodiment). That is, the HST 1 functionsas one component of the power train for vehicle between power source 300and the driving axle. The HST 1 includes hydraulic pump unit 10,hydraulic motor unit 20, PTO unit 30 and HST housing 40. The hydraulicpump unit 10 has pump shaft 11 extending in the fore-aft direction ofthe vehicle with an end away from the driving axle (rear end 11 b inthis embodiment) operatively connected to the drive power source 300.The hydraulic motor unit 20 has motor shaft 21 extending in the fore-aftdirection of the vehicle and is designed to output the drive powerthrough the motor shaft 21 whose speed is non-stepwisely varied incooperation with the hydraulic pump unit 10. The PTO unit 30 has PTOshaft 31 extending in the fore-aft direction of the vehicle andoperatively connected to the pump shaft 11. The HST housing 40accommodates the hydraulic pump unit 10, hydraulic motor unit 20 and PTOunit 30.

The HST housing 40 has center section 41 adapted to support thereon thehydraulic pump unit 10 and the hydraulic motor unit 20 and formingtherein a hydraulic circuit for hydraulic connection between both units10, 20, and housing body 42 connected to the center section 41 so as toenclose the hydraulic pump unit 10, the hydraulic motor unit 20 and thePTO unit 30. In this embodiment, a pair of hydraulic lines 101 areemployed as the hydraulic circuit formed in the center section 41.

In this embodiment as illustrated in FIG. 3, the center section 41 formsa part of the wall (front wall) of the HST housing 40 closer to thedriving axle. This center section 41 may also be designed to form a wall(rear wall) away from the driving axle.

At least one of the hydraulic pump unit 10 and the hydraulic motor unit20 is designed to be of a variable displacement type enabling thevariation of the inflow/outflow amounts of hydraulic fluid. In thisembodiment, the hydraulic pump unit 10 is of the variable displacementtype, while the hydraulic motor unit 20 is of a fixed displacement type.In this respect, it is a matter of course to employ the arrangement withthe hydraulic pump unit of the fixed displacement type and the hydraulicmotor unit of the variable displacement type, or with both the units ofthe variable displacement type.

The hydraulic pump unit 10 includes pump shaft 11, piston unit 12,cylinder block 13, output adjusting member 14, and control shaft 15 (seeFIG. 8 and the other Figures). The pump shaft 11 has rear end libextending rearwards through the housing body 42 to be operativelyconnected with the power source 300 and front end 11 a extendingforwards through the center section 41. The piston unit 12 rotatesaround the axis of the pump shaft 11 as a result of the rotation of thepump shaft 11 and reciprocates in association with this rotation. Thecylinder block 13 reciprocably supports the piston unit 12 while beingsupported by the center section 41 in such a manner as to be incommunication with the pair of hydraulic lines 101. The output adjustingmember 14 is designed to vary the amount of inflow/outflow by the pistonunit 12 through limiting the stroke length of the piston unit 12 basedupon its tilting position. The control shaft 15 is designed to adjustthe tilting position of the output adjusting member 14.

Since this embodiment employs an axial piston type pump unit as thehydraulic pump unit 10, a movable swash plate is employed to function asthe output adjusting member 14. Accordingly, where a radial piston typehydraulic pump unit is employed, a cam ring is employed as the outputadjusting member.

The hydraulic motor unit 20 of the fixed displacement type includescylinder block 23 that is supported on the center section 41 in such amanner as to be in communication with the pair of hydraulic lines 101,piston unit 22 that is slidably supported within the cylinder block 23,and reciprocable and rotatable by pressurized hydraulic fluid from thepair of hydraulic lines 101, and motor shaft 21 that is rotatable aroundthe axis as a result of the rotation of the piston unit 22, therebyenabling the rotational output adjusted according to the outputadjusting member 14 to be outputted through the motor shaft 21.

As illustrated in FIG. 1, the vehicle of this embodiment is providedwith a mechanical transmission 320 as a transfer device for providing awide range of speed change of the driving axle, in which the mechanicaltransmission 320 transfers the drive power between the HST 1 serving asthe main speed change device and differential device 350 with front axle310 serving as the main driving axle mounted therein. Because of this,the motor shaft 21 forwardly extends through the center section 41 tohave forward end 21 a connected to the mechanical transmission 320.

The mechanical transmission 320 may include for example driving shaft321 that is connected to the motor shaft 21 in such a manner as to berelatively non-rotatable around the axis, clutch member 322 that isrelatively non-rotatably and axially slidably supported on the drivingshaft 321, idle gear 323 that is relatively rotatably supported on thedriving shaft 321 and adapted to be selectively engaged with anddisengaged from the clutch member 322 according to the axial slide ofthe clutch member 322, driven shaft 324 that is disposed parallel withthe driving shaft 321, first driven gear 325 that is relativelynon-rotatably supported on the driven shaft 324 to be meshed with theidle gear 323, second driven gear 326 that is relatively non-rotatablysupported on the driven shaft 324, output shaft 327 that is disposedcoaxially with the motor shaft 21 and operatively connected to the frontaxle 310 via the differential gear device 350, output gear 328 that isrelatively non-rotatably supported on the output shaft 327 to be meshedwith the second driven gear 326 and adapted to be selectively engagedwith and disengaged from the clutch member 322 according to the axialslide of the clutch member 322, and casing 340 for accommodating thesemembers.

According to the mechanical transmission 320 having the abovearrangement, the clutch member 322 is selectively engaged with theoutput gear 328 or the driving gear 323, thereby providing two differentrotational speed stages to the output shaft 327.

The mechanical transmission 320 is preferably provided with second PTOunit 330, as illustrated in FIG. 1.

The second PTO unit 330 may include for example counter shaft 331disposed parallel with the driven shaft 324, PTO gear 332 that isrelatively rotatably supported on the counter shaft 331 to be meshedwith the first driven gear 325, second PTO clutch member 333 that isselectively engaged with and disengaged from the PTO gear 332, andsecond PTO shaft 334 that relatively non-rotatably supports the secondPTO clutch member 333 and has a rear end extending rearwards.

The second PTO unit 330 provided can easily take off the drive-powersynchronized with the front axle 310 serving as the main driving axle.Therefore, in the cases such as that a rear axle (not shown) besides thefront axle 310 is to be driven, it is possible to constantly rotatethese axles synchronously to each other without necessity of acomplicated transmission mechanism.

The mechanical transmission serving as a transfer device between the HSTand the differential device will be hereinafter described in moredetail. FIG. 10 is a perspective view of an area extending from the HST1 to the front axle 310 as viewed obliquely from behind.

As illustrated in FIG. 10, the mechanical transmission 320 is providedon an upper portion thereof with range shift arm 341 a for shifting theclutch member 322 of the mechanical transmission 320, and shifting arm341 b for the shifting the second PTO clutch member 333. The range shiftarm 341 a and the shifting arm 341 b are coupled respectively tomanipulating members mounted on a driver's stand such as mechanicaltransmission manipulating lever La and second PTO unit manipulatinglever Lb.

A reference code 43 in FIG. 10 represents speed change arm 43 fortilting and rotating the output adjusting member of HST 1. The speedchange arm 43 has a first end connected to speed change pedal P or anyother manipulation member on the driver's stand via a wire or the likeand a second end connected to the output adjusting member 14.Accordingly, the speed change arm is rotated in response to theoperator's manipulation of the manipulation member, thereby tilting androtating the output adjusting member.

FIGS. 11 and 12 illustrate cross sectional plan views of the mechanicaltransmission 320. Specifically, FIGS. 11 and 12 are cross-section takenalong the drive-power transmission path of the mechanical transmission320, and cross-section including a moving part of the range shift arm341 a. FIG. 13 is a longitudinal cross-section of the mechanicaltransmission 320 with its stepped cross-section as viewed from behind.

The mechanical transmission 320 is detachably interconnected between theHST 1 and the differential device 350. Specifically, the casing 340 ofthe mechanical transmission 320 is designed to be detachablyinterconnected to the HST housing 40 of the HST 1 and differentialhousing 351 of the differential device 350, respectively.

In the arrangement with the mechanical transmission 320 removed, it ispossible to couple the motor shaft 21 of the HST 1 to the differentialdevice 350. That is, the output shaft 327 of the mechanical transmission320 is disposed coaxially with the motor shaft 21 of the HST 1(hereinafter referred to main drive-power transmission axis (ML)), sothat the motor shaft 21 can be directly connected to the differentialdevice 350 in the arrangement with the mechanical transmission removed.

Specifically, when mounting the mechanical transmission 320, fourelongated bolts G are screwed into the front side of the differentialhousing 351 of the differential device 350, passing the HST housing 40and the casing 340 of the mechanical transmission 340, so that they areinterconnected (see FIG. 10). In this manner of use, the driving shaft321 of the mechanical transmission 320 is connected to the motor shaft21 of the HST 1 in such a manner as to be relatively non-rotatable withrespect to the axis, while the output shaft 327 of the mechanicaltransmission 320 is connected to power input part 352 of thedifferential device 350 via bevel gear 327 a.

On the other hand, when the mechanical transmission 320 is out of use,the HST 1 can be connected directly to the differential device 350 ofthe HST 1. In this manner of use, the motor shaft 21 of the HST 1 isconnected to the power input part 352 of the differential device viabevel gear 327 a′ having the same arrangement as the bevel gear 327 a(see FIG. 14).

The casing 340 includes body 340 a that supports the driving shaft 321,the output shaft 327 and the driven shaft 324, and extension 340 b thatextends from the body 340 a and past the HST 1 in the directionperpendicular to the main drive-power transmission axis ML. The secondPTO shaft 334 is supported on this extension 340 b. This arrangement cansimplify the power train between the second PTO shaft 334 and thesubsequent members.

The shifting operation of the mechanical transmission 320 will behereinafter described in more detail.

As illustrated in FIG. 11, the driving shaft 321 is disposed coaxiallywith the motor shaft 21 and connected thereto in such a manner as to berelatively non-rotatable with respect to the axis. An end of the drivingshaft 321 is relatively rotatably positioned in the rear side of theoutput shaft 327. That is, the output shaft 327 is disposed coaxiallywith the driving shaft 321, and loosely supported for the relativerotation with respect to the axis.

The clutch member 322 is relatively non-rotatably and axially slidablysupported on the driving shaft 321 between the idle gear 323 relativelyrotatably supported on the driving shaft 321 and the output gear 328relatively non-rotatably supported on the output shaft 327.

More specifically, the clutch member 322 includes spline hub 322 a thatis relatively non-rotatably fitted around the driving shaft 321, andsleeve 322 b that is relatively non-rotatably and axially slidablyfitted around the spline hub 322 a.

The idle gear 323 and the output gear 328 respectively have engagingelements 323 a and 328 a on portions adjacent to the spline hub 322 awith the same pitch as that of a spline formed on the outercircumference of the spline hub 322 a.

Accordingly, through the axial sliding motion of the sleeve 322 b, itcan take a position enabling engagement with the spline hub 322 a only(hereinafter referred to neutral position), a position enablingengagement with both the spline hub 322 a and the engaging element 323 a(hereinafter referred to low speed position), and a position enablingengagement with the spline hub 322 a and the engaging element 328 a(hereinafter referred to high speed position).

More specifically, the idle gear 323 and the first driven gear 325 eachhave a particular number of teeth (pitch circle diameter) set so thatthe rotational speed of the driving shaft 321 is reduced atpredetermined speed reducing ratio R and transmitted to the driven shaft324. Also, the second driven gear 326 and the output gear 328 each havea particular number of teeth set so that the rotational speed of thedriven shaft 324 is reduced at predetermined speed reducing ratio R andtransmitted to the output shaft 327.

That is, the number of teeth of each gear is set so that the speedreducing ratio of the first driven gear 325 with respect to the idlegear 323 and that of the output gear 328 with respect to the seconddriven gear 326 are: R.

With the sleeve 322 b at the low speed position, the drive power of thedriving shaft 321 is transmitted to the output shaft 327 via the idlegear 323, first driven gear 325, driven shaft 324, second driven gear326 and output gear 328. Therefore, when the rotational speed of thedriving shaft 321 is: V, the output shaft 327 is rotated at a rotationalspeed of V/R².

On the other hand, with the sleeve 322 b at the high speed position, thedriving shaft 321 is directly connected to the output shaft 327 with thesleeve 322 b. Therefore, when the rotational speed of the driving shaft321 is: V, the output shaft 327 is also rotated at a rotational speed ofV.

The description of the operation mechanism of the sleeve 322 b will behereinafter made with reference mainly to FIGS. 12 and 13.

As illustrated in FIG. 12, supporting shaft 342 parallel with the maindrive-power transmission axis ML is supported on the casing 340, onwhich selector fork 343 is axially slidably supported. The selector fork343 includes driving part 343 a and passive part 343 b that extend awayfrom each other in the radial direction from the connected portion withthe supporting shaft 342. The driving part 343 a has an end engaged withthe sleeve 322 b. The driving part 343 a forms therein a hollowedportion with a closed end. The hollowed portion with the closed endopens to a through-hole, through which the supporting shaft 342 extends,and extends in the direction orthogonal to the through-hole. Thehollowed portion is provided therein with ball 345 and helicalcompression spring 344 that biases the ball 345 towards the supportingshaft 342. The supporting shaft 342 forms thereon dished recesses 342L,342N, 342H along a direction from the idle gear 323 to the output gear328 respectively for receiving the ball 345. The ball 345 engages witheither recess to prevent unexpected movement of the selector fork 343,and retreats to the inside of the hollowed portion against the biasingforce of the spring 344 when the selector fork 343 is forced to slide onthe supporting shaft 342. The ball 345 is then positioned on a differentrecess of those recesses with the biasing force of the spring 344 toprevent the unexpected movement of the selector fork 343.

The range shift arm 341 a above the casing 340 has a rotational shaftextending into the casing 340. A driving arm 346 is connected to anextended portion of the rotational shaft inside of the casing. Thedriving arm 346 extends in the direction orthogonal to the rotationalshaft and has an end engaging with the passive part 343 b.

More specifically, the passive part 343 b has a U-shape with an openend, and is connected to the driving arm 346 via an engaging pin 347positioned between the legs of the U-shaped passive part 343 b. Withthis arrangement, the rotational shaft is rotated around the axisthereof by the rotation of the range shift arm 341 a around therotational shaft, so that the driving arm 346 is rotated around therotational shaft. This rotation of the driving arm 346 allows thepassive part 343 b (selector form 343) to slide along the supportingshaft 342.

Thus, the sliding movement of the selector fork 343 along the supportingshaft 342 causes the movement of the sleeve 322 b engaged with theselector fork 343, which enables the sleeve to take the neutralposition, low speed position or high speed position. More specifically,when the ball 345 engages with each of the recesses 342L, 342N, 342H ofthe supporting shaft 342, the sleeve 322 b correspondingly takes the lowspeed position enabling the engagement with both the spline hub 322 aand the engaging element 323 a, neutral position enabling the engagementwith the spline hub 322 a only, and high speed position enabling theengagement with both the spline hub 322 a and the engaging element 328a.

Now, the description of the second PTO unit 330 will be made in moredetail with reference mainly to FIGS. 11 and 12.

As illustrated in FIG. 11, the counter shaft 331 and the second PTOshaft 334 are disposed coaxially with each other in such a manner as tobe relatively rotatable with each other around the axis.

The PTO gear 332 includes cylindrical body 332 a supported on thecounter shaft 331 via one-way clutch 365. The cylindrical body 332 a isprovided thereon with external gear portion 332 b that is meshed withthe first driven gear 325 and internal gear portion 332 c.

The second PTO clutch member 333 includes cylindrical slider 333 a thatis relatively non-rotatably and axially slidably supported on thecounter shaft 331 and the second PTO shaft 334. Specifically, the slider333 a has an internal gear portion that is meshed with a spline providedon the each-other-facing portions of the counter shaft 331 and thesecond PTO shaft 334, so that it can take a position enabling theengagement with both the counter shaft 331 and the second PTO shaft 334,and a position enabling the disengagement from the counter shaft 331.

The slider 333 a also has external gear portion 333 b that is engagedwith the internal gear portion 332 c of the cylindrical body 332 a, andannular groove 333 c for axial sliding of the slider in the axialdirection.

The shifting arm 341 b has a rotational shaft extending into the casing340. A driving arm 361 is connected to an extended portion of therotational shaft inside of the casing. The driving arm 361 extends inthe direction orthogonal to the rotational shaft and has an end engagingwith the annular groove 333 c of the slider 333 a.

Accordingly, the rotation of the shifting arm 341 b around therotational shaft causes the rotation of the rotational shaft around theaxis, and hence the rotation of the driving arm 361 around therotational shaft. Thus, the slider 333 a slides along the counter shaft333 a and the second PTO shaft 334 in response to the rotation of thedriving arm 361.

Now, the description of the shifting action of the second PTO unit 330will be described in more detail.

Firstly, with the slider 333 a at position A illustrated in FIG. 11, thedrive power is transmitted from the first driven gear 325 to the secondPTO shaft 334 via the second PTO gear 332 and the slider 333 a. That is,with the slider 333 a at the position illustrated in FIG. 11, the secondPTO unit 330 is drawn into a forcible output mode.

Secondly, with the slider 333 a at position B illustrated in FIG. 11,the second PTO gear 332 is released from engaging relationship with theslider 333 a, while the counter shaft 331 is brought into connectionwith the second PTO shaft 334 via the slider 333 a in such a manner tobe relatively non-rotatable around the axis. As described above, thesecond PTO gear 332 is supported on the counter shaft 331 via theone-way clutch 365. Accordingly, with the slider 333 a at the positionB, semi-output mode becomes effective, enabling the interruption of thetransmission of the drive power from the second PTO gear 332 to thecounter shaft 331 in the case where the rotation number of the secondPTO shaft 334 exceeds that of the second PTO gear 332.

Lastly, with the slider 333 a at position C illustrated in FIG. 11, theslider 333 a is disengaged from the counter shaft 331. Accordingly,non-output mode becomes effective, enabling non-output of the drivepower through the second PTO shaft 334.

When the drive power for the rear wheels is to be taken off through thesecond PTO shaft 334, the second PTO shaft 334 is preferably rotated insynchronization with the output shaft 327. For this purpose, thefollowing arrangement is employed in this embodiment. That is, thetransmission ratio from the driven shaft 324 to the counter shaft 331 orthe second PTO shaft 334 is set to be the same as the transmission ratiofrom the driven shaft 324 to the output shaft 327.

Specifically, the second PTO gear 332 is designed so that the speedreducing ratio of the second PTO gear 332 with respect to the firstdriven gear 325 can be the same as the speed reducing ratio R of theoutput gear 328 with respect to the second driven gear 326. Thereby, thesecond PTO shaft 334 is rotated in synchronization with the output shaft327 regardless of the shifting state of the mechanical transmission 320.

That is, with the mechanical transmission 320 in a low speed state orwith the sleeve 322 b at the low speed position, the driven shaft 324 isrotated at a speed of V/R via the idle gear 323 and the first drivengear 325 when the driving gear 321 is rotated at a rotational speed ofV. The output shaft 327 is also rotated at a speed of V/R² via thesecond driven gear 326 and the output gear 328. At this moment, thesecond PTO gear 332 has a gear ratio of R with respect to the firstdriven gear 325, so that the second PTO gear 332 is rotated at a speedof V/R² likewise the output shaft 327.

With the mechanical transmission 320 in a high speed state or with thesleeve 322 b at the high speed position, the output shaft 327 is rotatedat a speed of V that is the same as the rotational speed of the drivingshaft 321. The driven shaft 324 is also rotated at a speed of R×V viathe output gear 328 and the second driven gear 326. At this moment, thesecond PTO gear 332 has a gear ratio of R with respect to the firstdriven gear 325, so that the second PTO gear 332 is rotated at a speedof V likewise the output shaft 327.

In this embodiment, the second PTO shaft 334 is thus rotated insynchronization with the output shaft 327 regardless of the shiftingstate of the mechanical transmission.

The second PTO gear 332 is meshed with the first driven gear 325 in thisembodiment. However, the present invention is not necessarily limited tothis embodiment. Rather, various embodiments can be employed as far asthe speed change ratio from the driven shaft 324 to the counter shaft331 or the second PTO shaft 334 is the same as the speed change ratiofrom the driven shaft 324 to the output shaft 327. For example, it ispossible to employ an arrangement that enables the second PTO gear 332to be meshed with the second driven gear 326.

In the above description, the mechanical transmission 320 that iscapable of selectively performingspeed-change-and-power-transmission/power-shutdown between the HST 1 andthe differential device is employed as the transfer device between theHST 1 and the differential device. However, the present invention is notnecessarily limited to this embodiment.

For example, where the speed change between the HST and the differentialdevice is not needed, a constant speed transmission device may beemployed as the transfer device, as illustrated in FIG. 15. In thefollowing description on the constant speed transmission deviceillustrated in FIG. 15, same or identical parts to those of themechanical transmission 320 have been given the same referencecharacters to omit a detailed description thereof.

As illustrated in FIG. 15, in the constant speed transmission device,the driving shaft 321 and the output shaft 327 are coupled to each othervia cylindrical coupling member 322′ in such a manner as to beconstantly non-rotatable with respect to each other around the axis.

The drive power to the second PTO gear is transmitted from the drivingshaft 321 via the idle gear 323 and the first driven gear 325. Each gearis set so that the second PTO shaft is rotated in synchronization withthe output shaft.

Specifically, it is possible to employ the arrangement with the idlegear 323, the first driven gear 325 and the second PTO gear 332 allhaving the same number of teeth, or the arrangement with the firstdriven gear 325 designed to increase or decrease the speed at apredetermined speed change ratio with respect to the idle gear and thesecond PTO gear 332 designed to increase or decrease the speed at thesame speed change ratio as the predetermined speed change ratio withrespect to the first driven gear 325.

Now, the description of the PTO unit 30 will be made. The PTO unit 30includes PTO shaft 31 that is disposed in the fore-aft direction of thevehicle and has front end 31 a extending forwardly through the frontwall of the HST housing 40, and hydraulic clutch device 32 that isdesigned for on/off of the drive power transmission from the pump shaft11 to the PTO shaft 31.

The hydraulic clutch device 32 includes first gear 32 a that isrelatively non-rotatably supported on the pump shaft 11, driving gearmember 32 b that is relatively rotatably supported on the PTO shaft 31to be meshed with the first gear 32 a, driving-side clutch plate 32 cthat is relatively non-rotatably and axially non-slidably supported onthe driving gear member 32 b, driven-side clutch plate 32 d that isdisposed opposite to the driving-side clutch plate 32 c, pressing member32 e that is relatively non-rotatably and axially slidably supported onthe PTO shaft 31 in such a manner as to relatively non-rotatably supportthe driven-side clutch plate 32 d and bring the same into engagementwith the driving-side clutch plate 32 c by the effect of hydraulicpressure, and biasing member 32 f that biases the pressing member 32 ein such a manner as to move the driven-side clutch plate 32 d away fromthe driving-side clutch plate 32 c. According to this arrangement, thePTO shaft 31 is rotated in synchronization with the pump shaft 11 uponreceiving the effect of the hydraulic pressure.

Brake device 33 is preferably provided to apply braking power on the PTOshaft 31 in association with power shutdown action of the hydraulicclutch device 32 to the PTO shaft 31. The brake device 33 provided caneffectively prevent the PTO shaft 31 from rotating with the moment ofinertia effected by the working device connected to the PTO shaft 31when shutting down the drive power transmission to the PTO shaft 31.

The HST 1 according to this embodiment additionally includes charge pumpunit 50 for feeding pressurized hydraulic fluid to the pair of hydrauliclines The charge pump unit 50 includes charge pump body 51 of a trochoidgear type that is supported on front extension 11 a of the pump shaft11, and charge pump case 52 that is connected to a wall of the HSThousing 40 closer to the driving axle, enclosing the charge pump body51. In this embodiment, the center section 41 corresponds to this wall.

The charge pump case 52 includes center portion 52 a that forms thereina hereinafter described hydraulic line communicated with an inlet portand an outlet port of the charge pump body 51, and projection 52 b thatprojects from the center portion 52 a and extends in the vehicle widthdirection towards the outside. The projection 52 b is designed toprovide bearing support for the front end 31 a of the PTO shaft 31.

By providing the bearing support for the front end 31 a of the PTO shaft31 through the charge pump case 52, the following effects can beprovided.

In comparison with distance D (i.e., the distance between the front wallof the HST housing and the driving axle) in the arrangement with themechanical transmission interposed between the HST and the driving axle(FIG. 1) and the distance D in the arrangement without the mechanicaltransmission (FIG. 9a), the former is longer than the latter by L2 ofthe length of the mechanical transmission 320 with respect to thefore-aft direction of the vehicle.

Therefore, in order to have the distance between the driving axle andthe front end of the PTO shaft constant in the respective arrangements,it is necessary to have the front end of the PTO shaft further extendingtowards the front side of the vehicle from the HST housing. However,simply extending the front end of the PTO shaft may result in rotationaldeflection of the PTO shaft or the like.

On the contrary, in this embodiment, since the front end 31 a of the PTOshaft 31 is bearing-supported by the charge pump case 52, the rotationaldeflection can effectively be prevented even in the arrangement with thefront end 31 a of the PTO shaft 31 further extending from the HSThousing 40.

In this embodiment, the HST is designed so that the front end 31 a ofthe PTO shaft 31 can be supported by the HST only. Specifically, thefront end 31 a of the PTO shaft 31 is supported by the charge pump case52 that is a constituent member of the HST 1, so that improvedassembling efficiency is obtainable as compared with the arrangementwith the front end of the PTO shaft supported by a separate member suchas a vehicle body other than the HST.

The HST 1 having the above arrangement preferably includes auxiliarypump unit 60 of an external gear type that is detachably mountedthereon. FIG. 5 is a view as viewed along lines V—V in FIG. 3.

As illustrated in FIGS. 3 and 5, the auxiliary pump unit 60 may includefirst pump gear 61 that is relatively non-rotatably supported on aportion of the front end 11 a of the pump shaft 11, which portionforwardly extends from the charge pump case 52, second pump gear 62 thatis meshed with the first pump gear 61, idle shaft 63 that supportsthereon the second pump gear 62, and auxiliary pump case 64 that isconnected to the charge pump case 52, enclosing the first and secondpump gears 61, 62.

By providing the auxiliary pump unit 60, it is possible to provide asufficient amount of pressurized hydraulic fluid according to thespecification of each vehicle without applying an excessive load on thecharge pump unit 50. Specifically, where the vehicle is designed toenable the mower to elevate, and/or where a power steering device isprovided for the steering wheels, the auxiliary pump unit 60 providedcan make the charge pump unit 50 available for feeding the pressurizedhydraulic fluid to the pair of hydraulic lines 101 and the hydraulicclutch device 32 in the PTO unit 30, and make the auxiliary pump unit 60available for feeding the pressurized hydraulic fluid to the mowerelevation device and/or the power steering device, thereby preventingexcessive load to the charge pump unit 50, while providing a sufficientamount of the pressurized hydraulic fluid.

The description will be hereinafter made for the hydraulic circuit ofthe HST 1.

FIGS. 6 and 7 are respectively cross-sections taken along lines VI—VIand VII—VII in FIG. 3. FIG. 8 is a view as viewed along lines VIII—VIIIin FIG. 3.

As illustrated in FIGS. 2 and 6, the charge pump case 52 is providedwith inlet line 102 having a first end opening to the outside and asecond end connected to inlet port 61 a of the charge pump body 51, andpressurized fluid line 104 having a first end connected to outlet port51 b of the charge pump body 51 and a second end branched to firstpressurized fluid line 105 and second pressurized fluid line 106 viaflow divider 103 and then opening to the outside. The first end of theinlet line 102 is in communication with hydraulic fluid tank 400 viapipe fitting 140 (see FIGS. 2, 5 and 6).

As illustrated in FIGS. 2 and 7, the center section 41 to be connectedto the charge pump case 52 is provided with the pair of hydraulic lines101, first bypass line 110 for communication between the pair ofhydraulic lines 101, charge line 111 having a first end communicatedwith the first pressurized fluid line 105 and a second end connected tothe first bypass line 110, charge relief valve 112 interposed in thecharge line 111, and pair of high pressure relief valves 113 and pair ofcharge check valves 114, which pairs are interposed in the first bypassline 110 between its connection point to the charge line 111 and itsconnection point to the pair of hydraulic lines 101.

The center section 41 is preferably and additionally provided withsecond bypass line 115 for communication between the pair of hydrauliclines 101, drain line 116 having a first end communicated with thesecond bypass line 115 and a second end communicated with the hydraulicfluid tank, and pair of suction valves 117 interposed in the secondbypass line 115 between its connection point to the drain line 116 andits connection point to the pair of hydraulic lines 101. By providingthe pair of suction valves 117, it is possible to prevent the generationof negative pressure in the pair of hydraulic lines 101 in the casewhere a vehicle stops on a slope with its engine stopped, and henceprevent the vehicle from rolling down on the slope (freewheeling).

As illustrated in FIGS. 2 and 4, the center section 41 is also providedwith pressurized fluid feeding line 120 having a first end communicatedwith the second pressurized fluid line 106 and a second end opening tothe inside of the HST housing 40.

The second end of the pressurized fluid feeding line 120 is communicatedwith PTO hydraulic line 122 formed in the rear wall of the HST housing42 via conduit 121 disposed within the HST housing 121.

As illustrated in FIGS. 2 and 4, the HST housing 42 is provided with thePTO hydraulic line 122 having a first end connected to the conduit 121and a second end connected to the hydraulic clutch device 32, reliefvalve 123, electromagnetic switching valve 124 and accumulator 125respectively interposed in the PTO hydraulic line 122, and drain line126 communicated with the electromagnetic switching valve 124.

The auxiliary pump case 64 is provided as illustrated in FIGS. 2 and 5with third pressurized fluid line 130 passing through a meshing portionbetween the first pump gear 61 and the second pump gear 62 and havingopposite ends opening to the outside.

Of the opposite ends of the third pressurized fluid line 130, first end130 a is connected via suitable conduit to a housing of the differentialdevice 350, which housing also serves as the hydraulic fluid tank 400,so that the third pressurized fluid line 130 supplies the pressurizedhydraulic fluid through second end 130 b to hydraulic circuit 200 forelevation of the mower and actuation of the power steering device (seeFIG. 2). The return fluid from the circuit 200 passes the inside of theHST housing 40 through a hydraulic fluid cooler, and then returns to thehydraulic fluid tank 400. Reference code 410 in FIG. 2 represents acommon filter.

While the description in this embodiment was made by taking for examplethe case where the front axle 310 acts as the main driving axle and thePTO shaft 31 extends to the front side with respect to the fore-aftdirection of the vehicle, the present invention is not necessarilylimited to this embodiment. Rather, the present invention is alsoapplicable to the arrangement where the rear axle acts as the maindriving axle and the PTO shaft extends to the rear side with respect tothe fore-aft direction of the vehicle.

The HST 1 is preferably provided with neutral return mechanism 480 forbiasing the output adjusting member 14 to the neutral position inresponse to the tilting and rotating action of the output adjustingmember 14 in the vehicle advancing direction or vehicle reversingdirection. The vehicle advancing direction and vehicle reversingdirection respectively mean the tilting or rotating directions thatgenerate the rotational outputs respectively moving the vehicle forwardand rearward.

The description will be herein made for the neutral return mechanism480. FIG. 16 is a cross-section taken along lines XVI—XVI in FIG. 3.

As illustrated in FIGS. 8 and 16, the control shaft 15 includes body 15a that is relatively rotatably supported on the housing 40 while beingnon-rotatable with respect to the output adjusting member 14, and outerextension 15 b that outwardly extends from the body 15 a to the outsideof the housing 40, so that the tilting and rotating position of theoutput adjusting member 14 can be changed from the outside of thehousing 40. That is, the output adjusting member 14 can be tilted androtated through the rotation of the outer extension 15 b of the controlshaft 15 around the axis.

In this embodiment, the speed change arm 43 is connected to the outerextension 15 b of the control shaft 15, and the free end of the speedchange arm 43 is connected to the speed change pedal P disposed closerto a driver seat via a suitable connection member (not shown), asillustrated in FIGS. 10 and 16.

The control shaft 15 and the output adjusting member 14 may beintegrally formed with each other, or separately formed while having amechanism allowing the associated operation with each other.

The housing 40 preferably forms therein opening 40 a through which theoutput adjusting member (movable swash plate in this embodiment) 14 canpass. By forming the opening 40 a, it is possible to have the controlshaft 15 and output adjusting member 14 connected or formed integrallywith each other and mounted within the housing 40. In this arrangement,the clearance between the inner circumference of the opening 40 a andthe outer circumference of the control shaft 15 may be sealed byplate-like lid 40 b with a bearing boss.

FIGS. 17 and 18 are cross sections taken along lines XVII—XVII in FIG. 8with the output adjusting member 14 set at the neutral position and themaximum output position in the vehicle advancing direction.

As illustrated in FIGS. 8 and 16-18, the neutral return mechanism 480includes torsion spring 481 that is supported around the outer extension15 b of the control shaft 15, and detent pin 482 that lies at referenceposition N when the output adjusting member 14 is at the neutralposition, and tilts and rotates in the X and Y-directions around theaxis of the control shaft 15 by a displacement amount corresponding to atilted and rotated position of the output adjusting member 14 when theoutput adjusting member 14 tilts and rotates in the vehicle advancingdirection and reversing direction.

In this embodiment, the detent pin 482 has proximal end 482 a connectedto the output adjusting member 14 and distal end 482 b extendingoutwardly from circular slot 40 c formed in the lid 40 b (see FIGS. 8and 17-18), while both ends of the torsion spring 481 lie respectivelyon the both sides of the distal end 482 b with respect to the movingdirection thereof (see FIGS. 17 and 18).

With the above arrangement, the detent pin 482 presses first end 481 aand second end 481 b of the torsion spring 481 against its biasing forcethrough its pivotal movement in the vehicle advancing direction (Xdirection) and reversing direction (Y direction).

The neutral return mechanism 480 includes fixing member 483 for fixingthe second end 481 b and first end 481 a of the torsion spring 481 inposition during the pivotal movement of the detent pin 482 in thevehicle advancing direction and reversing direction. Specifically, thefixing member 483 is adapted to limit the movement of the second end 481b of the torsion spring 481 during the detent pin 482 presses the firstend 481 a of the torsion spring 481, and limit the movement of the firstend 481 a of the torsion spring 481 during the detent pin 482 pressesthe second end 481 b of the torsion spring 481.

In this embodiment, the neutral return mechanism 480 includes covermember 485 that is attached on the outer surface of the lid 40 b tocover over the torsion spring 481 and the detent pin 482, therebyeffectively preventing the intrusion of impurities such as dusts intothe housing. A fixing pin to be fixed to the cover member 485 is used asthe fixing member 483.

The fixing pin 483 is preferably an eccentric pin having body 483 a tobe interposed between the both ends 481 a and 481 b of the torsionspring 481, and an eccentric part 483 b outwardly extending with itsaxis eccentric to the axis of the body 483 a. Whereby, the relativeposition of the body 483 a to the control shaft 15 can be varied throughthe rotation of the eccentric part 483 b around the axis of the body 483a and hence adjustment of the output adjusting member 14 to the neutralposition after assembling of the HST can easily be performed.

The neutral return mechanism 480 also includes auxiliary device 490 thatbiases the detent pin 482 to the reference position N during the pivotalmovement of the detent pin 482.

As illustrated in FIGS. 17 and 18, the auxiliary device 490 includescylindrical casing 491 fixed on the cover member 485 with an outer endpositioned outside of the cover member 485, push pin 492 that is axiallyslidably placed in the cylindrical casing 491 with a distal end of thepush pin 492 abuttable against the detent pin 482 by the pivotalmovement of the detent pin 482, lid member 493 that seals the outer endof the cylindrical casing 491, and biasing spring 494 that is disposedbetween a distal end of the push pin 492 and the lid member 493.

The auxiliary device 490 is disposed so that the axial direction of thepush pin 492 is substantially matched to the pivoting direction of thedetent pin 482. That is, the auxiliary device 490 is designed so thatthe detent pin 482 presses the push pin 492 in the axial directionagainst the biasing force of the biasing spring 494 during the pivotalmovement of the detent pin 482 from the reference position N in thevehicle advancing direction (X direction) and/or the vehicle reversingdirection (Y direction), as illustrated in FIG. 18.

The lid member 493 is preferably fixed on the cylindrical casing 491 insuch a manner as to be adjustably positioned along the axis of thecylindrical casing 491. With this arrangement, the biasing force of thebiasing spring 494 can be suitably adjusted.

According to the HST 1 having the above arrangement, when the driverreleases the manipulating member such as the manipulation lever (notshown) operatively connected to the output adjusting member 14 from theengaged state, the output adjusting member 14 automatically and promptlyreturns to the neutral position. Therefore, the braking distance forstopping the vehicle can be shortened by efficiently utilizing a dynamicbrake by the HST 1.

That is, when the driver tilts or rotates the output adjusting member 14in the vehicle advancing direction or reversing direction via themanipulating member and the control shaft 15, the detent pin 482pivotally moves against the biasing forces effected by two biasingmembers, namely the torsion spring 481 supported around the controlshaft and the biasing spring 494 of the auxiliary device 490.Accordingly, the driver's releasing action causes the detent pin 482 toreturn to the reference position N by the biasing forces of both thetorsion spring 481 and the biasing spring 494, so that the outputadjusting member 14 promptly returns to the neutral position.

Where the HST has the movable swash plate as the output adjusting member14 and employs a so-called shoe-type arrangement that the movable swashplate and the axial piston unit are connected together via universaljoint 16 (see FIG. 16), a self-return moment of the movable swash platefor returning to the neutral position is small so that this arrangementis particularly effective for the desirable effect as mentioned above.

Since the auxiliary device 490 is of a simple arrangement that has onlythe push pin 492 and the biasing spring 494 as main components, it ispossible to produce the above desirable effect, while not inviting thelarge-sizing and complexity of the entire HST.

It is preferable to limit the tilting or rotating range of the outputadjusting member 14, thereby effectively preventing excessive increasein vehicle speed. In this embodiment, the housing 40 forms therein theslot 40 c defining the pivoting range of the detent pin 482, so that theslot 40 c limits the pivoting range of the detent pin 482 or the tiltingrange of the output adjusting member 14. More preferably, the outputadjusting member 14 has a smaller tilting range in the vehicle reversingdirection than in the vehicle advancing direction, so that the maximumspeed in the vehicle reversing direction can effectively be limited.

The arrangement for limiting the tilting range of the output adjustingmember 14 may be varied. For example, it is possible to provide in thehousing 40 a pair of stoppers that are abuttable to the output adjustingmember 14.

The auxiliary device 490 may be selectively provided on either one orboth of a vehicle advancing side and reversing side of the detent pin482 for a desirable arrangement. Specifically, openings 485 a for theattachment of the auxiliary device are respectively formed in the wallson the vehicle advancing side and the vehicle reversing side of thedetent pin 482 in the cover member 485, so that the auxiliary device 490can be selectively attached in place without needs of separateoperations or parts for obtaining a suitable arrangement. Accordingly,if it is desired to prevent the abrupt stop of the vehicle, theauxiliary device 490 may be provided only on the vehicle advancing sideof the detent pin 482.

With the arrangement as described above, where the detent pin ispivotally movable around the control shaft in association with thetilting action of the output adjusting member in the variabledisplacement type unit, and during the tilting of the detent pin fromthe reference position, the detent pin is biased towards the referenceposition through the biasing force of the auxiliary device as well asthe biasing force by the torsion spring supported on the control shaft,the output adjusting member automatically and promptly returns to theneutral position once the driver releases the output adjusting memberfrom the operational mode. Therefore, the dynamic brake action by theHST can promptly and effectively be produced at the time of stopping thevehicle, and therefore the braking distance of the vehicle can beshortened.

By having the auxiliary device acting only during the vehicle runs inthe advance direction, it is possible to effectively prevent sudden stopof the vehicle when the vehicle runs in the reverse direction.

By employing the auxiliary device including the pressing memberabuttable against the detent pin and the biasing member biasing thedetent pin towards the reference position via the pressing member duringthe pivotal movement of the detent pin, the above desirable effects canbe produced through such a remarkably simple structure.

When the biasing member is a spring having the distal end abuttedagainst the pressing member and the proximal end supported by abiasing-force adjusting member, which can be fixed at a given positionalong the axis along which the spring is compressed and expanded, it ispossible to properly adjust the biasing force effected by the spring tothe detent pin. Accordingly, the dynamic brake action by the HST can beproperly adjusted according to preference.

In this embodiment, the auxiliary pump unit 60 is provided in additionto the charge pump unit 50, where the charge pump unit 50 is used forfeeding pressurized hydraulic fluid to the pair of hydraulic lines 101and the hydraulic clutch device 32 in the PTO unit 30, while theauxiliary pump unit 60 is used for feeding the pressurized hydraulicfluid to the mower elevation device and/or the power steering device.This arrangement thus enables the feeding of a large amount ofpressurized hydraulic fluid, but may invite cost increase due to theincreased number of pumps.

To address the above, where a relatively small amount of hydraulic fluidto be fed is acceptable, only a single charge pump unit 50′ may be used,thereby achieving the feeding of the pressurized hydraulic fluid tothose three devices, while reducing the costs involved.

FIG. 19 is a transverse plan view of HST 1′ equipped only with thecharge pump unit 50′. FIGS. 20 and 21 are cross-sections taken alonglines XX—XX and XXI—XXI in FIG. 19. Further, FIG. 22 is a hydrauliccircuit diagram of the vehicle to which the HST 1′ is applied. In thefollowing description on the embodiment illustrated in FIGS. 19 to 22,same or identical parts to those of this embodiment have been give thesame reference characters to omit a detailed description thereof.

As illustrated in FIG. 19, the charge pump unit 50′ includes charge pumpbody 51′ that is driven through the front extension 11 a of the pumpshaft 11, and charge pump case 52′ that is connected to the HST housing40 while supporting thereon the charge pump body 51′.

The charge pump case 52′ includes central part 52 a′ that forms thereina herein described hydraulic line into which the pressurized hydraulicfluid flows from the charge pump body 51′, and extension 52 b′ thatextends from the central part 52 a′ outwardly with respect to thevehicle width direction, so that the front extension 31 a of the PTOshaft 31 can be bearing-supported by the extension 52 b′.

The charge pump case 52′ is provided with inlet line 103′ that receivesthe pressurized hydraulic fluid from the charge pump body 51′ via filter102 a′, pressurized fluid charge line 105′ and pressurized fluid line109′ for the hydraulic device that are branched from the inlet line 103′via branching part 104′, pressure reducing valve 107′ that is mounted inthe pressurized fluid charge line 105′ to set a charging hydraulicpressure, pressurized fluid line 106′ for the PTO that receives asurplus fluid discharged through the pressure reducing valve 107′, andresistive valve 108′ that is mounted in the pressurized fluid line 109′for the hydraulic device.

The pressurized fluid charge line 105′ is communicated with the chargeline 111 via the filter 102 b′. The pressurized fluid line 106′ for thePTO is communicated with the hydraulic line 122 for the PTO via thehydraulic fluid feeding line 120 and the conduit 121. The pressurizedfluid line 109′ for the hydraulic device is opened in the rear side ofthe charge pump case 52′ and is communicated with the hydraulic circuit200 for the working device via a suitable conduit.

This specification is by no means intended to restrict the presentinvention to the preferred embodiments set forth therein. Variousmodifications to the hydrostatic transmission and the power train forvehicle, as described herein, may be made by those skilled in the artwithout departing from the spirit and scope of the present invention asdefined in the appended claims.

What is claimed is:
 1. A power train for vehicle between a driving powersource and a driving axle comprising: a transfer device being detachablyinterconnected between a main speed change device that is operativelyconnected to the driving power source and a differential gear devicethat transmits the drive power to the driving axle; wherein saidtransfer device, when interconnected between said main speed changedevice and said differential gear device, includes a driving shaft andan output shaft, said driving shaft being disposed along a maindrive-power transmission axis and operatively connected to a main outputshaft of said main speed change device, said main transmission axisbeing coaxial with said main output shaft, and said output shaft beingdisposed along said main drive-power transmission axis for outputtingthe drive power to the differential gear device, wherein the speed canbe stepwisely changed between the driving shaft and the output shaft;and wherein when said transfer device has been detached, said mainoutput shaft of said main speed change device is directly connected tosaid differential gear device.
 2. A power train for vehicle between adriving power source and a driving axle comprising: a transfer devicedisposed between a main speed change device that is operativelyconnected to the driving power source and a differential gear devicethat transmits the drive power to the driving axle; said transfer deviceincluding a driving shaft and an output shaft, said driving shaft beingdisposed along a main drive-power transmission axis and operativelyconnected to a main output shaft of said main speed change device, saidmain transmission axis being coaxial with said main output shaft, andsaid output shaft being disposed along said main drive-powertransmission axis for outputting the drive power to the differentialgear device, wherein the drive power is transmitted between the drivingshaft and the output shaft; said transfer device including an extensionextending past the main speed change device in the direction orthogonalto the main drive-power transmission axis, a PTO shaft supported on saidextension in such a manner as to be substantially parallel to the maindrive-power transmission axis, and a drive-power transmission mechanismfor transmitting the drive power synchronized with the output shaft tothe PTO shaft; wherein said drive-power transmission mechanism includes:a driven shaft that is disposed between the main drive-powertransmission axis and the PTO shaft in parallel thereto; a first geartrain for transmitting the drive power from the driving shaft to thedriven shaft at a predetermined speed reducing ratio; a second geartrain for transmitting the drive power from the driven shaft to theoutput shaft at the same speed reducing ratio as said predeterminedspeed reducing ratio; and a third gear train for transmitting the drivepower from the driven shaft to the PTO shaft at the same speed reducingratio as said predetermined speed reducing ratio; said first gear trainincluding an idle gear that is relatively rotatably supported on thedriving shaft, and a first driven gear that is relatively non-rotatablysupported on the driven shaft to be meshed with said idle gear; saidsecond gear train including a second driven gear that is relativelynon-rotatably supported on the driven shaft, and an output gear that isrelatively non-rotatably supported on the output shaft to be meshed withsaid second driven gear; said third gear train including a PTO gear thatis meshed with either one of said first and second driven gears totransmit the drive power to the PTO shaft; wherein the speed reducingratio of the first driven gear with respect to the idle gear, the speedreducing ratio of the output gear with respect to the second drivengear, and the speed reducing ratio of the PTO gear with respect to thefirst or second driven gear are the same; said transfer device includinga counter shaft that is disposed coaxially with the PTO shaft and aslider that is relatively non-rotatably and axially slidably supportedon said PTO shaft and said counter shaft; said PTO gear being supportedon the counter shaft via a one way clutch; and said slider is adapted toselectively take a non-outputting position enabling disconnectionbetween the counter shaft and the PTO shaft, a forced outputtingposition enabling connection between the counter shaft and the PTO shaftwhile being in meshing engagement with the PTO gear, and a middleposition between the non-outputting position and the forced outputtingposition, enabling connection between the counter shaft and the PTOshaft while being out of the meshing engagement with the PTO gear.
 3. Apower train for vehicle between a driving power source and a drivingaxle comprising: a transfer device being detachably interconnectedbetween a main speed change device that is operatively connected to thedriving power source and a differential gear device that transmits thedrive power to the driving axle; said transfer device including adriving shaft and an output shaft, said driving shaft being disposedalong a main drive-power transmission axis and operatively connected toa main output shaft of said main speed change device, said maintransmission axis being coaxial with said main output shaft, and saidoutput shaft being disposed along said main drive-power transmissionaxis for outputting the drive power to the differential gear device,wherein the drive power is transmitted between the driving shaft and theoutput shaft; said transfer device including an extension extending pastthe main speed change device in the direction orthogonal to the maindrive-power transmission axis, a PTO shaft supported on said extensionin such a manner as to be substantially parallel to the main drive-powertransmission axis, and a drive-power transmission mechanism fortransmitting the drive power synchronized with the output shaft to thePTO shaft; and wherein when said transfer device has been detached, saidmain output shaft of said main speed change device is directly connectedto said differential gear device.
 4. A power train according to claim 3,wherein said drive-power transmission mechanism includes: a driven shaftthat is disposed between the main drive-power transmission axis and thePTO shaft in parallel thereto; a first gear train for transmitting thedrive power from the driving shaft to the driven shaft at apredetermined speed reducing ratio; a second gear train for transmittingthe drive power from the driven shaft to the output shaft at the samespeed reducing ratio as said predetermined speed reducing ratio; and athird gear train for transmitting the drive power from the driven shaftto the PTO shaft at the same speed reducing ratio as said predeterminedspeed reducing ratio.
 5. A power train according to claim 4, wherein:said first gear train includes an idle gear that is relatively rotatablysupported on the driving shaft, and a first driven gear that isrelatively non-rotatably supported on the driven shaft to be meshed withsaid idle gear; said second gear train includes a second driven gearthat is relatively non-rotatably supported on the driven shaft, and anoutput gear that is relatively non-rotatably supported on the outputshaft to be meshed with said second driven gear; said third gear trainincludes a PTO gear that is meshed with either one of said first andsecond driven gears to transmit the drive power to the PTO shaft; andwherein the speed reducing ratio of the first driven gear with respectto the idle gear, the speed reducing ratio of the output gear withrespect to the second driven gear, and the speed reducing ratio of thePTO gear with respect to the one of the first and second driven gearwith which it is meshed are the same.
 6. A power transmission accordingto claim 5, wherein: said transfer device includes a counter shaft thatis disposed coaxially with the PTO shaft and a slider that is relativelynon-rotatably and axially slidably on said PTO shaft and said countershaft, said PTO gear being supported on the counter shaft via a one wayclutch; and said slider is adapted to selectively take a non-outputtingposition enabling disconnection between the counter shaft and the PTOshaft, a forced outputting position enabling connection between thecounter shaft and the PTO shaft while being in meshing engagement withthe PTO gear, and a middle position between the non-outputting positionand the forced outputting position, enabling connection between thecounter shaft and the PTO shaft while being out of the meshingengagement with the PTO gear.
 7. A power train according to claim 4,wherein: said transfer device includes a clutch member that isrelatively non-rotatably and axially slidably supported on the drivingshaft; and said clutch member is adapted to selectively take a positionenabling connection between the driving shaft and an idle gear, aposition enabling connection between the driving shaft and the outputshaft, and a neutral position between the position enabling connectionbetween the driving shaft and the idle gear and the position enablingconnection between the driving shaft and the output shaft, enablingshutdown of the drive-power transmission from the driving shaft to theoutput shaft.